1. Technical Field
This invention relates generally to transportable shelters and containers (hereinafter “containers”) and, more particularly, to containers that satisfy international and military standards and regulations regarding stackability, including International Standards Organization (ISO), Container Safety Convention (CSC), and Coast Guard Certification (CGC) standards.
2. History of the Related Art
Containers suitable for transportation by truck, ship, or air must generally comply with the standards and regulations for ship freight set forth by ISO and CSC. Furthermore, containers that are transported by helicopter must be able to support the dynamic load imposed by the lifting of the containers, which is typically about three times the static load. Heretofore, such containers generally have a metal framework, i.e., a post-and-beam construction, with composition board (usually steel or aluminum sheathed) or other composite material panels attached to the framework by bolts, rivets, welding, and the like. Such containers, however, are inherently heavy. For example, a standard 20-feet long container constructed to meet ISO size requirements (typically 8 feet wide by 8 feet high) weighs on the order of 4,000 to 5,000 pounds. As a result, the maximum cargo or payload that can be transported in such a container is generally limited to two to three times the tare weight, or empty weight, of the container. Furthermore, the side, roof, and floor panels of the metal-framed container typically do not support any structural loads or provide any structural resistance to externally applied forces. The metal framework of these containers must therefore have sufficient mass and structural strength to support both the cargo load and any externally applied forces.
Metal-framed and paneled containers also have different thermal expansion characteristics for the various materials used in the construction of the containers. Metal framework typically expands or contracts at a rate that is different than the expansion or contraction rate of the panels. This difference in thermal expansion characteristics is particularly significant in extreme temperature environments where the joints between the panels and the metal frame can become stressed or cracked, permitting the entrance of moisture and water into the joints. Also, for panels having metal surfaces, the surfaces tend to expand and contract at a rate that is different from the rate of the underlying core, resulting in delamination of the panels.
More recently, instead of metal framework, some transportable containers that have been constructed to meet ISO size requirements have been formed of composite material panels. However, clips or other fastening means must be used to hold these composite material panels in their respective relative positions. For example, U.S. Pat. No. 5,285,604, issued Oct. 10, 1991 to Kevin Carlin, discloses a mobile kitchen formed of composite material walls that is assembled from modular components and then held together by rivets extending through aluminum bolsters bridging one or more of the components. However, as stated in this patent, while the aluminum rivet bolster strips are advantageous for securing the riveted connections between panels, they do not provide substantial additional rigidity, support, or structural strength for the panels. Thus, the Carlin structure is inherently incapable of supporting or resisting vertically or transversely applied forces of any significant magnitude. In other words, the structure is not stackable, i.e., it cannot support another similar unit stacked on top of it and is inherently weak in resisting transversely applied loads.
It would be desirable to be able overcome the problems set forth above. In particular, it would be desirable to have a transportable container constructed of lightweight materials in which the walls, roof, and floor of the container are structural load bearing members that also have similar coefficients of expansion. It would also be desirable to have such a container that has a payload capability greater than eight to nine times its tare weight. Furthermore, it would be desirable to have a container that is capable of providing a barrier to electromagnetic signals, or, alternatively, can be constructed of a material that is not reflective of radar energy. It is also desirable to have a container that is capable of being pressurized and maintained at a positive pressure atmosphere to prevent the infiltration of hazardous, toxic, or otherwise undesirable atmospheres, or for high altitude applications.